Jellyfish tentacles have tiny stinging cells that they use to stun their prey and defend against predators. Jellyfish stings can be painful to humans and sometimes dangerous, particularly box jellyfish. Stings can occur while wading, swimming or diving in salt water. Jellyfish do not go after humans but if someone brushes up against one – or even steps on a dead one – they can be stung. While jellyfish stings can be painful, most are not emergencies. The main symptoms are pain, burning and redness at the sting site. Red lines are common.
* Properly research the areas you intend to dive.
* Minimize unprotected areas. Always wear full wetsuits, hoods, boots and gloves. Something as simple as nylon pantyhose worn over the skin will prevent jellyfish stings.
* Carry sufficient household vinegar with you to all dive sites.
If stung by any jellyfish, follow these procedures:
1. Apply household vinegar to the area. Generously pour or spray the area with vinegar for no less than 30 seconds to neutralize any invisible remnants. Let the vinegar stand for a few minutes before doing anything else.
2. Wash the area with seawater or saline (do not use freshwater). Use a syringe with a steady stream of water to help remove any tentacle remains. Do not rub the affected area or put ice on a sting.
3. Apply heat. After you remove the tentacles, soak the affected area in hot water (104-113 F or 40-45 C) for 30 to 90 minutes.
Seek emergency attention if:
The person displays signs of a severe allergic reaction.
The sting is from a box jellyfish.
The sting covers more than half an arm or leg.
Source: Divers Alert Network (DAN) and WebMD.com